1. Field of the Invention
The present invention relates to olefin polymerization and to the preparation of polyolefin products. In particular the present invention relates to the preparation of a variety of polyolefin products using a liquid phase polymerization process. In this latter regard, the invention relates to a novel liquid phase process for the polymerization of olefins using a modified BF3 catalyst which is stabilized with a complexing agent.
2. The Prior Art Background
The polymerization of olefins using Friedel-Crafts type catalysts, including BF3, is a generally known procedure. The degree of polymerization of the products obtained varies according to which of the various known polymerization techniques is used. In this latter regard, it is to be understood that the molecular weight of the polymeric product is directly related to the degree of polymerization and that the degree of polymerization may be manipulated by manipulating process parameters so as to produce a variety of products having respective desired average molecular weights.
Generally speaking, due to the nature and mechanics of the olefinic polymerization process, a polyolefin product has a single double bond remaining in each molecule at the end of the polymerization process. The position of this remaining double bond is often an important feature of the product. For example, polyisobutylene (PIB) molecules wherein the remaining double bond is in a terminal (vinylidene) position are known to be more reactive than PIB molecules wherein the remaining double bond is internal, that is, not in a terminal position. A PIB product wherein at least 50% of the double bonds are in a terminal position may often be referred to as high vinylidene or highly reactive PIB. The extent to which a polyolefin product has terminal double bonds may also be manipulated by manipulation of process parameters.
Current processes for olefin oligomerization often employ BF3/co-catalyst systems wherein the BF3 is complexed with a co-catalyst. This is done for a variety of reasons that are well known to those skilled in the olefin polymerization field. For example, and as is explained in U.S. Pat. No. 5,408,018, a complexed BF3 catalyst may be useful for manipulating and attempting to balance the molecular weight, vinylidene content and polydispersity of PIB. The co-catalyst often is propanol or a higher alcohol and such co-catalyst systems are used irrespective of whether the desired product is a poly alpha olefin or a poly internal olefin. However, the use of alcohols having beta hydrogen atoms in such co-catalyst complexes is troublesome because, over time, the BF3 tends to attack the beta hydrogen atoms. This leads to decomposition of the alcohol whereby the catalyst is rendered ineffective. Thus, the co-catalyst complex is unstable and often has a very short shelf life.
To address this problem, many current processes employ a procedure whereby the co-catalyst complex is prepared in-situ by mixing the alcohol and gaseous BF3 immediately prior to introduction of the co-catalyst complex into a reactor. In addition, it is not unusual in the conduct of processes employing such co-catalyst systems to use an excess of alcohol and to sparge gaseous BF3 into the reaction mass at several downstream points to rebuild catalyst activity. Such methodology implies a three-phase reaction and the necessity of using a stirred tank reactor to provide means of dispersing gaseous BF3 into the reaction mass. These processes use either batch reactors or a set of continuously stirred tank reactors in series to provide both gas handling capability and to satisfy the necessity for a plug flow reactor configuration.
It is also known that alpha olefins, particularly PIB, may be manufactured in at least two different grades—regular and high vinylidene. Conventionally, these two product grades have been made by different processes, but both often and commonly use a diluted feedstock in which the isobutylene concentration may range from 40-60% by weight. More recently it has been noted that at least the high vinylidene PIB may be produced using a concentrated feedstock having an isobutylene content of 90% by weight or more. Non-reactive hydrocarbons, such as isobutane, n-butane and/or other lower alkanes commonly present in petroleum fractions, may also be included in the feedstock as diluents. The feedstock often may also contain small quantities of other unsaturated hydrocarbons such as 1-butene and 2-butene.
Regular grade PIB may range in molecular weight from 500 to 1,000,000 or higher, and is generally prepared in a batch process at low temperature, sometimes as low as −50 to −70° C. AlCl3, RAlCl2 or R2AlCl are used as catalysts. The catalyst is not totally removed from the final PIB product. Molecular weight may be controlled by temperature since the molecular weight of the product varies inversely with temperature. That is to say, higher temperatures give lower molecular weights. Reaction times are often in the order of hours. The desired polymeric product has a single double bond per molecule, and the double bonds are mostly internal. Generally speaking, at least about 90% of the double bonds are internal and less than 10% of the double bonds are in a terminal position. Even though the formation of terminal double bonds is believed to be kinetically favored, the long reaction times and the fact that the catalyst is not totally removed, both favor the rearrangement of the molecule so that the more thermodynamically favored internal double bond isomers are formed. Regular PIB may be used as a viscosity modifier, particularly in lube oils, as a thickener, and as a tackifier for plastic films and adhesives. PIB can also be functionalized to produce intermediates for the manufacture of detergents and dispersants for fuels and lube oils.
High vinylidene PIB, a relatively new product in the marketplace, is characterized by a large percentage of terminal double bonds, typically greater than 70% and preferentially greater than 80%. This provides a more reactive product, compared to regular PIB, and hence this product is also referred to as highly reactive PIB. The terms highly reactive (HR-PIB) and high vinylidene (HV-PIB) are synonymous. The basic processes for producing HV-PIB all include a reactor system, employing BF3 and/or modified BF3 catalysts, such that the reaction time can be closely controlled and the catalyst can be immediately neutralized once the desired product has been formed. Since formation of the terminal double bond is kinetically favored, short reactions times favor high vinylidene levels. The reaction is quenched, usually with an aqueous base solution, such as, for example, NH4OH, before significant isomerization to internal double bonds can take place. Molecular weights are relatively low. HV-PIB having an average molecular weight of about 950-1050 is the most common product. Conversions, based on isobutylene, are kept at 75-85%, since attempting to drive the reaction to higher conversions reduces the vinylidene content through isomerization. Prior U.S. Pat. No. 4,152,499 dated May 1, 1979, U.S. Pat. No. 4,605,808 dated Aug. 12, 1986, U.S. Pat. No. 5,068,490 dated Nov. 26, 1991, U.S. Pat. No. 5,191,044 dated Mar. 2, 1993, U.S. Pat. No. 5,286,823 dated Jun. 22, 1992, U.S. Pat. No. 5,408,018 dated Apr. 18, 1995 and U.S. Pat. No. 5,962,604 dated Oct. 5, 1999 are all directed to related subject matter.
U.S. Pat. No. 4,152,499 describes a process for the preparation of PIBs from isobutylene under a blanket of gaseous BF3 acting as a polymerization catalyst. The process results in the production of a PIB wherein 60 to 90% of the double bonds are in a terminal (vinylidene) position.
U.S. Pat. No. 4,605,808 discloses a process for preparing PIB wherein a catalyst consisting of a complex of BF3 and an alcohol is employed. It is suggested that the use of such a catalyst complex enables more effective control of the reaction parameters. Reaction contact times of at least 8 minutes are required to obtain a PIB product wherein at least about 70% of the double bonds are in a terminal position.
U.S. Pat. No. 5,191,044 discloses a PIB production process requiring careful pretreatment of a BF3/alcohol complex to insure that all free BF3 is absent from the reactor. The complex must contain a surplus of the alcohol complexing agent in order to obtain a product wherein at least about 70% of the double bonds are in a terminal position. The only reaction time exemplified is 10 minutes, and the reaction is carried out at temperatures below 0° C.
In addition to close control of reaction time, the key to obtaining high vinylidene levels seems to be control of catalyst reactivity. This has been done in the past by complexing BF3 with various oxygenates including sec-butanol and MTBE. One theory is that these complexes are actually less reactive than BF3 itself, disproportionately slowing the isomerization reaction and thus allowing for greater differentiation between the vinylidene forming reaction (polymerization) and the isomerization reaction rates. Mechanisms have also been proposed that suggest the BF3 complexes are non-protonated and thus are not capable of isomerizing the terminal double bond. This further suggests that water (which can preferentially protonate BF3) must generally be excluded from these reaction systems. In fact, prior publications describing preparation of PIB using BF3 complexes teach low water feed (less than 20 ppm) is critical to formation of the high vinylidene product.
HV-PIB is increasingly replacing regular grade PIB for the manufacture of intermediates, not only because of higher reactivity, but also because of developing requirements for “chloride free” materials in the final product applications. Important PIB derivatives are PIB amines, PIB alkylates and PIB maleic anhydride adducts.
PIB amines can be produced using a variety of procedures involving different PIB intermediates which provide a reactive site for subsequent amination. These intermediates may include, for example, epoxides, halides, maleic anhydride adducts, and carbonyl derivatives.
Reference to HV-PIB as “highly reactive” is relative to regular grade PIB. HV-PIB is still not, in absolute terms, highly reactive toward formation of some of these intermediates. Other classes of compounds, polyethers for example, can be much more reactive in the formation of amines and amine intermediates. Amines derived from polyethers are known as polyether amines (PEAs) and are competitive products to PIB amines.
The use of HV-PIB as an alkylating agent for phenolic compounds, is triggered by the higher reactivity and higher yields achievable with HV-PIB. These very long chain alkyl phenols are good hydrophobes for surfactants and similar products.
The largest volume PIB derivatives are the PIB-maleic anhydride reaction products. HV-PIB is reacted with maleic anhydride through the double bond giving a product with anhydride functionality. This functionality provides reactivity for the formation of amides and other carboxylate derivatives. These products are the basis for most of the lube oil detergents and dispersants manufactured today. As mentioned above, PIB-maleic anhydride products can also be used as intermediates in the manufacture of PIB amine fuel additives.
Other polyolefins which are commercially useful for a variety of purposes include conventional PIB wherein the vinylidene content is less than 50%, low molecular weight (<350 and perhaps even <250) oligomers of branched monomers such as isobutylene, oligomers and higher molecular weight polymers of linear C3-C15 alpha olefins, and oligomers and higher molecular weight polymers of linear C4-C15 non-alpha (internal double bond) olefins. Although these materials are all well known to those skilled in the olefin polymerization field, there is always a need for new developments which improve process efficiency and/or product qualities and reduce operating costs and/or capital expenditures.